In recent years, washing processing by which organic contaminant adhering to a surface to be irradiated by light is removed, or oxide-film formation processing by which an ultra-thin oxide film is formed on a surface to be processed, by irradiating vacuum ultraviolet radiation having a wavelength of, for example, 200 nm or less, to various work pieces to be processed.
An excimer discharge lamp in which excimer molecules, such as xenon molecules, are generated by using dielectric barrier electric discharge thereby emitting excimer light is widely used as an irradiation source of the vacuum ultraviolet radiation.
The background art of such an excimer discharge lamp is disclosed in, for example, Japanese Laid Open Patent No. H02-007353. Specifically, a radiator in which an electric discharge container is filled up with electric discharge gas, and excimer molecules are formed by the presence of dielectric material whereby light emitted from the excimer molecules is taken out, is disclosed therein. The electric discharge intervened by the dielectric material is also called ozonizer electric discharge or silent electric discharge. Refer to “Electric Discharge Handbook, revised new edition” 7th edition, page 263, resold Jun., 1989, published by Institute of Electrical Engineers of Japan.
A dielectric barrier discharge lamp light source apparatus is disclosed in Japanese Laid Open Patent No. H11-204280, may be related art to the present invention. According to the Japanese Laid Open Patent, in order to obtain efficient excimer light emission, a leading edge of a waveform of an AC voltage impressed to the lamp needs to be steep. A flyback, a half bridge, or a full bridge type inverter can be used for a circuit in order to realize it.
Moreover, Japanese Laid Open Patent No. H11-260581 discloses that it is possible to ease conditions of the steepness of a leading edge of an AC voltage waveform which is needed for the AC voltage impressed to a lamp, and also it is possible to reduce the peak current of a switching element of an inverter, and further a half bridge, a full bridge, and a push pull type inverter can be used to realize a circuit therefore. Furthermore, it discloses that in order to realize a steep lamp voltage waveform, leakage inductance between primary and secondary coils of a boosting transformer of an inverter must be small.
Moreover, a high-frequency high-voltage transformer is disclosed in many references, such as Laid Open Utility Model Patent Nos. 53-071733, and 54-063114. Further, in these references, as a suitable flyback transformer, the technology of a double bobbin in which primary and secondary side coils are wound around separate bobbins and are assembled so that the bobbin for the secondary side coil may contain the bobbin for the primary side coil, and the technology using the bobbin for a section winding, are disclosed.
Furthermore, a boosting transformer of a discharge lamp lighting apparatus for an excimer discharge lamp is disclosed in, for example, Japanese Laid Open Patent No. 2005-039092. According to the reference, a gap layer between primary and secondary side coils is provided and further the gas layer between the primary and secondary side coils can be narrowed, while avoiding an undesirable phenomenon such as corona discharge in the transformer, and further, the energy transmission efficiency from the primary side coil to the secondary side coil can be improved, so that it is possible to realize steep voltage waveform applied to the lamp. Furthermore, it discloses that in order to realize a steep voltage waveform applied to a lamp, floating electrostatic capacity in the secondary side coil should be made small.
As disclosed in the references as to the conventional technology, efforts to make small the leakage inductance between the primary and secondary side coils of the boosting transformer of an inverter have been made, aiming at realization of efficient excimer light emission, as the highest priority objective. Moreover, although it is recognized that loss in the transformer can be reduced by making the floating electrostatic capacity in the transformer small, only measure has been taken to the extent that the leakage inductance between the primary and secondary side coils is not increased. Therefore, since technical development had been performed while reduction of the efficiency of a discharge lamp lighting apparatus is rather permitted, optimization in view of the total efficiency of a combination of the discharge lamp lighting apparatus and the excimer discharge lamp has not been considered.